Impact tools



p 3, 1968 E. F. KLESSIG ET AL 3,399,602

IMPACT TOOLS Filed Sept. 27, 1966 4 Sheets-Sheet 1 FIGI INVENTORS ERNST F. KLESSIG i 2 PETER 0. HANCOCK ff M Ma y 4%,, BY j ATTORNEYS,

Sept. 3, 1968 E. F. KLESSIG ETAL 3,399,602

IMPACT TOOLS Filed Sept. 27. 1966 4 Sheets-Sheet 3 FIG. 3 62 ,as l5 Sept. 3, 1968 E. F. KLESSIG ET AL 3,399,602

' IMPACT TOOLS Filed Sept. 27, 1966 4 Sheets-Sheet 4 FIG. 9

42 94 In no r 3,399,602 IMPACT TOOLS Ernst F. Klessig and Peter D. Hancock, Racine, Wis., assignors to Racine Hydraulics & Machinery, Inc., a corporation of Wisconsin Filed Sept. 27, 1966, Ser. No. 582,299 17 Claims. (Cl. 91235) This invention relates to impact tools and, more particularly, to a hydraulic hammer.

For many years, demolition work, such as concrete breaking, has been done by the use of air hammers. As is well-known, these hammers are noisy, with the noise being caused both by the air hammer as well as by the compressor for supplying air to the hammer. It has been found that this noise frequently damages the hearing of an operator of the air hammer after a period of time. Also, the air hammer delivers a great amount of shock to the body of the operator. From time to time, efforts have been made to develop a hydraulic device to replace the air hammer; however, prior known constructions have not delivered consistent and uniform blows because of erratic jumping of the body of the device, which has also been true of air hammers.

An object of this invention is to provide a new and improved impact tool and, more particularly, a hydraulic device, such as a hydraulic hammer, which substantially avoids the tendency to jump erratically and therefore delivers uniform, consistent impact blows, with a substantially reduced power input as compared to an air hammer for obtaining the same impact output.

Still another object of the invention is to provide a hydraulic hammer having a body with a piston-hammer movable therein with means for applying pressure liquid to the piston-hammer for obtaining the impact stroke thereof and with means on the piston-hammer providing for positive cut-off of the pressure liquid to the pistonhammer in advance of the actual impact blow by the piston-hammer, without requiring any shift of a control valve and resultant timing problems, with the result that erratic jumping of the body of the device is avoided.

Still another object of the invention is to provide a hydraulic impact device, such as a hydraulic hammer, wherein a movable piston-hammer has its direction of movement controlled by a control valve and wherein a reduction in pressure of the liquid acting on the pistonhammer during the impact stroke is used as a signal for shift of the control valve and with the shifting of the control valve resulting in supplying make-up liquid to the reduced pressure area to reduce reaction on the pistonhammer.

A further object of the invention is to provide a device as defined in the preceding paragraphs in which a bumper is positioned in the body of the device for possible contact by the piston-hammer at the end of its return stroke and with pressure liquid urging the bumper to an operative position whereby the bumper can yield when hit by the piston-hammer and also can yield during the return stroke, particularly during crossover of the directional control valve for the piston-hammer when the connection to tank is blocked.

An additional object of the invention is to provide a hydraulic hammer having a body, a piston-hammer with opposed pressure areas of different cross section reciprocable therein, valve means for controlling the direction of movement of the piston-hammer and having opposed differential pressure areas, means for continuously applying pressure fluid to the smaller pressure areas of the pistonharnmer and the valve means, with the valve means alternately applying pressure liquid to the larger pressure area of the piston-hammer to cause the impact stroke thereof,

nited States Patent C 3,399,692 Patented Sept. 3, 1958 ice and means including a land on the piston-hammer for cutting-off the supply of pressure liquid to the large pressure area of the piston-hammer while the valve means is still positioned to supply pressure liquid thereto to terminate the application of force to the piston-hammer in its impact stroke in advance of the actual impact blow and for connecting the large pressure area of the valve means to the large pressure area of the piston-hammer to permit decompression of liquid to cause shift of the valve means for causing return of the piston-hammer.

A further object of the invention is to provide a hydraulic hammer as defined in the preceding paragraph wherein a movable bumper is positioned in the body for contact by the piston-hammer at the end of the return stroke and with the bumper being loaded by pressure liquid to, in effect, function as an accumulator to take up shock and with the bumper also functioning as an accumulator during crossover of the valve means in advance of the change in direction of the piston-hammer, and the valve means embodying a hollow control valve member to permit flow of fluid therethrough and the differential pressure areas of the valve means being defined by two pairs of pins, with one pair being of a diameter larger than the other and engageable against the opposite ends of the valve member to provide the differential pressure areas while maintaining the valve member balanced.

Further objects and advantages will become apparent from the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 is a side elevational view of the hydraulic hammer embodying the invention;

FIG. 2 is a vertical section, on an enlarged scale, taken generally along the line 22 in FIG. 1;

FIG. 3 is a fragmentary view, similar to FIG. 2, showing the piston-hammer in a position immediately in advance of striking the impact blow;

FIG. 4 is a view similar to FIG. 3 showing the parts in a position occurring slightly after the position of FIG. 3 and with the control valve shifted;

FIG. 5 is a view similar to FIGS. 3 and 4 and showing the piston-hammer in one position during the return stroke immediately prior to shift of the control valve to change the application of force to the piston-hammer;

FIG. 6 is a section, on an enlarged scale, taken generally along the line 66 in FIG. 1;

FIG. 7 is a section, on an enlarged scale, taken generally along the line 77 in FIG. 1;

FIG. 8 is a section, taken generally along the line 88 in FIG. 2; and

FIG. 9 is a fragmentary view, corresponding to the lower left-hand part of FIG. 2, showing an open .center on-off control valve for the hammer.

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail an embodiment of the invention together With a modification thereof with the understanding that the present disclosure isto be considered as an exem-plification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated. The scope of the invention Will be pointed out in the appended claims.

The hydraulic hammer is shown generally in FIG. 1 and comprises a body made up of four interconnected parts connected end-to-end. An upper body part 10 is affixed to a central part 11 housing the control components for the hammer, with these body parts being interconnected by a series of attaching bolts 12. The central part 11 is connected to a body part 15 by a series of attaching bolts 16 and a lower tool-carrying part 17 of the body is yieldably connected to the body part 15 by a series of yieldable connectors in the form of bolts 18 which have springs 19 urging flanges 20 and 21 of the respective body parts 15 and 17 toward each other and against a spacer member 22 fitted between the flanges.

The hammer has a pair of handles 25 and 26 extending in opposite directions from the upper body part 10 whereby an operator can hold the hammer. A tool 27 extends from the lower body part 17 and is operative to perform the work of the hammer, such as demolition work in breaking of concrete. The hammer has two hose connections providing for operation thereof, with a first hose connectible to a port 30 for supplying fluid in the form of pressure liquid to the hammer and a second port 31 providing a connection to a second hose for returning fluid to tank.

The hydraulic hammer has a series of bores formed in the body part 11 with a first bore 35 mounting a pistonhammer 36 for movement back and forth therein and a second bore 37 mounting valve means in the form of a control valve member 38 for back and forth movement therein. A third bore 39 mounts a closed center on-olf control valve 40 for controlling the supply of pressure liquid to the piston-hammer 36 and valve member 38. The on-otf valve member 40 is urged to the closed position shown in FIG. 2 by a spring 41 engageable against an end thereof and urging the valve member against a control rod 42 engaging the opposite end and extending into an opening 43 in the top body part 10 where it can be engaged by a lever 44 extending parallel to and in overlying relation with the handle 26. The lever 44 is pivoted to the top body part 10 by a pivot pin 45. Upon depression of the lever 44, the valve 40 is shifted toward the right, as viewed in FIG. 2, by the rod 42 to shift a land 46 on the valve out of blocking relation and permit pressure liquid to flow from the inlet port 30 through the third bore 39 into a passage 47 in the central body part 11. The passage 47 has a pressure accumulator 48 threadably connected into an open end thereof, as indicated at 49. The accumulator can be of a gas type in which gas, under pressure behind a movable piston 50, functions to urge the piston outwardly of the accumulator or, optionally, can be a spring-loaded device. The piston 50 can move back and forth in response to pressure changes in the pressure liquid.

First passage means including the pass-age 47 supply pressure liquid to a part of the piston-hammer 36 and to the control valve member 38. The piston-hammer 36 has a land 51, with opposed differential pressure areas 52 and 53. The pressure area 52 is the larger, since it encompasses the entire end surface of the piston-hammer, while the area 53 is of a lesser size being an annular surface between the outer perimeter of the land 51 and the reduced shank portion 54 of the piston-hammer.

The control valve member 38 has a hollow interior -55 openable to both ends of the valve to permit quick flow-through of liquid and quick shifting of the valve member. The control valve member functions as a differential area valve, with a pair of large diameter movable control pins and 61 mounted in passages 60a and 61a in top body part 10 and engageable with one end of the valve member wall and a second. pair of smaller diameter movable control pins 62 and 63 mounted in body part 11 engageable with the opposite end of the valve member wall, with the operation thereof subsequently described.

The first passage means, previously referred to including the passage 47, continuously applies pressure liquid against the smaller pressure area 53 of the piston-hammer and the smaller diameter control pins 62 and 63, acting on the control valve member 38, whereby the pistonhammer and control valve member are both urged upwardly, or to the left as viewed in FIG. 2, during operation of the hammer. This first passage means includes a portion 65 of the bore 35, with flow past a raised rib 66 occurring as permitted by a reduced diam eter shank portion 67 of the piston-hammer. This latter 4 portion is of a diameter less than the piston-hammer land 51 whereby there can be free flow of pressure liquid past the rib 66 except at such time as the land 51 is aligned with the rib and, at which time, the passage is closed off because of the close fit therebetween. The first passage means further includes a continuation 68 of the passage 47 to supply pressure liquid to the rounded ends of the control pins 62 and 63, which transmit the force to the end of the control valve member 38 while still maintaining the control valve member in balanced condition. Second passage means, including a passage 70 in the body part 11 and a passage 71 in the body part 10 connect a port 72 opening into the bore or chamber 35 housing the piston-hammer with the large diameter pin passages 60a and 61a. Thus as shown in FIG. 2, with the first passage open past rib 66 into the bore 35 and with the piston-hammer land 51 positioned sufficiently far to the left, pressure liquid can flow through the second passage means to act against the control pins 60 and 61 to urge the control valve member 38 to the position shown in FIG. 2. Because of the greater pressure area of pins 60 and 61, the force acting constantly against pins 62 and 63 is overcome.

Third passage means, including a lateral passage 75, extends between an end of the bore 35 for the pistonhammer and the bore 37 for the control valve member 38 and subjects the large pressure area 52 of the pistonhammer either to pressure or tank, depending upon the position of the control valve member.

Fourth passage means in the form of a lateral passage 76 extends from the first bore 35 to the second bore 37 to supply pressure fluid to the third passage when the control valve member 38 is positioned as shown in FIG- 2 to cause the movement of the piston-hammer toward the right, as viewed in FIG. 2, in an impact stroke. The control valve member 38 has a pair of lands at opposite ends thereof with a reduced central section, with the land 77 functioning to either block the passage 76 from communication with the passage 75 or permit communication therebetween. The land 78 of the control valve member either blocks passage 75 from communication with tank or, when the control valve member shifts to the left from the position shown in FIG. 2, permits communication of the passage 75 with tank through an area 79 which communicates with the left-hand end of on-off valve bore 39, as viewed in FIG. 2. This end of bore 39 communicates with the tank port 31. The area 79 also communicates with a small accumulator mounted in the handle 25 having a movable piston 80 and a spring 81 to subject the tank line, through a passage 82, to accumulator action. During the impact stroke of the pistonhammer, this accumulator supplies flow to the return tank line to reduce pressure pulsation.

As shown in FIG. 2, a passage 85 provides a drain line from the right-hand end of the control valve bore 37.

A bumper is movably mounted to extend to an end of the piston-hammer bore 35 and is positioned within an opening 91 in the body part 11, with an enlarged rib 92 engageable around the edge of the opening 91 to limit inward movement of the bumper 90. This bumper is spring-urged toward the piston-hammer by a spring 93 and the back side of the bumper is supplied with pressure liquid through a passage 94 extending between the piston-hammer bore 35 and the back side of the bumper 98. A similar bumper is disclosed in an application of Ernst F. Klessig, Ser. No. 444,742, filed Apr. 1, 1965, now Patent Number 3,339,644.

The piston-hammer 36 has a hammer member 95 at the lower end thereof, or at the right as viewed in FIG. 2, for impact against an anvil 96 positioned within the spacer member 22, with the anvil engageable with an end of the tool 27. The anvil, when hit by the hammer 95, transmits the blow to the tool 27. A spacer 97 positions the anvil 96 at a distance from the hammer member to prevent double cycling.

The operation of the hydraulic hammer can now be described with particular reference to FIGS. 2 to 5. With the parts positioned as shown in FIG. 2, depression of the lever 44 opens the on-off valve 40 to supply pressure liquid to the first passage 47 and with the piston-hammer positioned as shown in FIG. 2, pressure liquid passes to the small and large pressure areas 53 and 52, respectively, of the piston-hammer because of the control valve member 38 being positioned toward the right and, thus, the piston-hammer descends in its impact stroke or toward the right, as viewed in FIG. 2. During this time, pressure liquid passes through port 72 and passages 70 and 71 to act on the control pins 60 and 61 to maintain the control valve member 38 shifted to the right position shown in FIG. 2. The piston-hammer has neared the end of its stroke, as shown in FIG. 3, with positive cut-off of pressure liquid to the large area 52 of the piston-hammer being effected by the land 51 coming into flow-blocking relation with the rib 66 in the bore 35 to block the first passage means. Thus, pressure liquid is no longer supplied to move the piston-hammer in the impact stroke, Without shift of the control valve member 38. Slight further movement of the piston-hammer toward the right, as viewed in FIG. 3, reduces the pressure in the bore 35 behind the piston-hammer land 51 and this reduced pressure reduces the pressure behind the control pins 60 and 61 by port 72 being opened to the reduced pressure area whereby small area control pins 62 and 63, which are continuously acted upon by pressure liquid take over and shift the control valve member 38 to the upper position, or left-hand position, as shown in FIG. 4. The retraction of the control pins 60 and 61 also results in supplying make-up fluid or liquid to the area of the bore 35 behind the large pressure area 52. In view of the foregoing, it will be seen that pressure liquid has been cutoff from the piston-hammer prior to the delivery of the blow to the anvil 96. Pressure liquid in the first passage acting continuously against the small pressure area 53 of the piston-hammer becomes eflective to raise the piston-hammer or move it to the left, as viewed in FIG. 4, with the area of the bore 35 behind the piston-hammer being connected to tank resulting from the shift of control valve member 38 which places passages 75 and 79 in communication because of the leftward shift of control valve member land 78. These passages are also subject to the action of accumulator piston 80 in handle 25, because of the cross-passages 1G0 in the wall of control valve member 38 which connect the interior thereof with the space 79 and with said valve interior communicating with the passage 82 in the upper body part 10.

During the return stroke of the piston-hammer, the land 51 functions to again shift the control valve member 38. More specifically, with the parts shown in the position of FIG. 5 during the return stroke, the port 72 is still blocked. Slight further leftward movement of the land 51 will open this port to pressure liquid which can flow through passages 70 and 71 to the large diameter control pins 60 and 61 and shift the control valve member back to the position shown in FIGS. 2 and 3. During shift of the control valve member 38 back to the position shown in FIG. 2, the land 78 will block communication between passages 75 and 79 so that the area behind the piston-hammer land 51 will be trapped. At this time, the bumper 90 is effective to provide accumulator action and can move backwardly as the piston-hammer continues its upward movement. Further, if the piston-hammer should physically contact the bumper 90, the bumper can yield upon impact because of its spring and pressure liquid loading. With the shift of the control valve member 38 back to the position shown in FIG. 2, the action reverses itself, with pressure liquid being applied to the large pressure area 52 of the piston-hammer and the cycle repeats itself.

With the structure as disclosed herein, the piston-hammer land 51 directly cuts off the supply of pressure liquid to the piston-hammer whereby the timing of operation is positive without requiring the shift of the control valve. This is particularly important Where pressure liquid is cut off prior to impact of the piston hammer with the anvil 96 to reduce the tendency for the body to bounce upon impact resulting from the velocity and pressure of the pressure liquid. Another important feature reducing the complexity of the construction is the use of the decompression signal in the pressure liquid behind the pistonhammer to effect shift of the control valve member 38. The trapped area behind the piston-hammer is opened to the large control pins 60 and 61 of the control valve member whereby the reduced pressure reduces the pressure on the control pins and the control valve member can shift. Liquid displaced by control pins 60 and 61 is supplied to the trapped area. This results in holding down the reaction on the piston-hammer and avoids detracting from the low struck on the anvil by the hammer.

The yieldable bumper provides accumulator action during control valve crossover and movement of the bumper creates pressure which is transmitted through the passage 94 back to the first passage means through communication with the bore 35 and the accumulator 48. Such forces as also may be encountered upon direct physical contact of the bumper by the piston-hammer are also transmitted back to the pressure liquid source by the same means so as to contribute to the forces applied to the piston-hammer in the next impact stroke. The action is further improved by the construction of the control valve member which, because of its being hollow, is light and permits large flow therethrough for quick shift and use of the control pins keeps the control valve member in balance.

In the event that the hammer is to be used with a constant displacement pump, the closed center on-off valve 40 may be replaced by an open center valve, as shown in FIG. 9. The open center valve member has a land 111 positioned to block flow to the first passage 47 and a land 112 arranged to permit flow to the tank side of the bore 39 when the valve member 110 is in off position. When the valve is shifted toward the right, the land 111 shifts to permit flow to the passage 47 and the land 112 shifts to a position to block flow to the tank side of the bore 39. This construction allows pressure liquid to bypass back to tank through the tank port 31 at a relatively low pressure drop when the on-ofl valve 110 is in the oft position.

We claim:

1. In an impact device, the combination comprising a body,

said body having a bore,

a piston-hammer reciprocable in said bore,

said piston-hammer having opposed pressure areas defining first and second pressure areas,

said first pressure area having an effective cross sectional area less than said second pressure area, means for continuously applying pressure fluid to said first pressure area,

valve means for alternately applying pressure fluid to said second pressure area and having opposed differential pressure areas,

means for continuously applying pressure fluid to the smaller of the pressure areas of the valve means,

and means including the piston-hammer for alternately connecting the larger of the pressure areas of the valve means to either pressure fluid or to a discharge path and for blocking pressure fluid from the second pressure area of the piston-hammer while the valve means is still positioned to supply pressure fluid thereto to terminate the application of force to the piston-hammer.

2. In an impact device as defined in claim 1 wherein said pistonhammer has a land for accomplishing said blocking of pressure fluid and is positioned on the pistonhammer to effect said blocking in advance of actual impact by said piston-hammer.

7 3. In a hydraulic impact device, the combination comprising a body, said body having a bore,

a piston-hammer reciprocable in said bore,

said piston-hammer having opposed pressure areas defining first and second pressure areas,

said first pressure area having an effective cross sectional area less than said second pressure area, mean for continuously applying pressure fluid to said first pressure area,

valve means for alternately applying pressure fluid to said second pressure area to impart the impact stroke to the piston-hammer and having opposed differential pressure areas, means for continuously applying pressure fluid to the smaller of the pressure areas of the valve means,

and means including a land on the piston-hammer operative on the impact stroke of the piston-hammer for connecting the larger of the pressure areas of the valve means to the second pressure area of the pistonhammer to permit shift of the valve means and for blocking pressure fluid from said second pressure area of the piston-hammer while the valve means is still positioned to supply pressure fluid thereto to terminate the application of force to the pistonhammer.

4. A hydraulic impact device as defined in claim 3 including a bumper positioned for contact by said pistonhammer on the return stroke thereof, and passage means bypassing said valve means for applying pressure fluid to said bumper to counteract impact forces thereagainst by said piston-hammer and function as an accumulator during crossover of said valve means.

5. A hydraulic impact device as defined in claim 4 including an inlet port, and an accumulator in communication with said inlet port and said passage means whereby the accumulator assists in absorbing the shock received by the bumper as transmitted by the pressure fluid.

6. A hydraulic impact device as defined in claim 3 wherein said land is positioned on the piston-hammer to effectively block the application of force in advance of actual impact by said piston-hammer.

7. A hydraulic impact device as defined in claim 3 wherein said valve means includes a valve body open from end-to-end, and said differential pressure areas are provided by a plurality of movable pins at opposite ends of the valve body engageable therewith, the pins at one end providing a greater total effective area than the pins at the other end.

8. In a hydraulic hammer, in combination, a body having a pair of chambers, a pressure liquid reciprocable differential area piston-hammer movably mounted in a first of said chambers, said piston-hammer having a large surface area portion and an opposing smaller surface area portion, a control valve member movably mounted in the second of said chambers, means associated with said valve member providing opposed differential areas subject to pressure liquid with a large area effective at one end of the valve member and a small area effective at the other end, first passage means for connection to a source of pressure liquid to apply pressure liquid continuously against the small effective area of the control valve member and the small area portion of the piston-hammer, second passage means connecting the first chamber with the large effective area of the control valve member, third passage means controlled by said control valve member for connecting the large surface area portion of the piston-hammer either to the source of pressure liquid or to tank, means on the piston-hammer operable during the impact stroke thereof to positively cut off the source of pressure liquid from said large surface area portion of the piston-hammer while the control valve is still positioned to connect the last mentioned area portion to said source and from the large effective area of the control valve member, and means for supplying make-up liquid to the large effective area of the piston hammer after said positive cut-off of fiow.

9. In a hydraulic hammer as defined in claim 8 Wherein said means for supplying make-up liquid includes said second passage means and a land on the piston-hammer whereby after said positive cut-off of flow said land opens said second passage means to the large surface area portion of the piston-hammer and reduction of pressure in said second passage means permits shift of the control valve member by the liquid pressure acting unopposed on the said small effective area of the control valve member and liquid flows from the large effective area of the control valve member through the second passage means to the first chamber.

10. In a hydraulic hammer as defined in claim 9 wherein said control valve member is hollow and open-ended to permit fluid flow therethrough while permitting quick shift thereof, and said means associated with the control valve member providing opposed differential areas comprises two pairs of pins with one pair engaging an end of the member to provide the small area, and the other pair of pins of a greater area providing the large area.

11. In a hydraulic device, in combination, a body having a pair of chambers, a pressure liquid reciprocable differential area piston-hammer movably mounted in a first of said chambers, said piston-hammer having a large surface area portion and an opposing small surface area portion, a control valve member movably mounted in the second of said chambers, means associated with said valve member providing opposed differential areas subject to pressure liquid with a large area effective at one end of the valve member and a small area efiective at the other end, first passage means for connection to a source of pressure liquid to apply pressure liquid continuously against the small effective area of the control valve member and the small area portion of the piston-hammer, second passage means connecting the first chamber with the large effective area of the control valve member, third passage means controlled by said control valve member for connecting the large surface area portion of the piston-ham mer either to the source of pressure liquid or to tank, means on the piston-hammer operable during the impact stroke thereof to positively cut off the source of pressure liquid from said large surface area portion of the pistonhammer and from the large effective area of the control valve member, and said piston-hammer after said positive cut-off of flow being effective to open the large effective area of the control valve member to the large surface area portion of the piston-hammer whereby continued movement of the piston-hammer reduces pressure acting on the large effective area of the control valve member to permit shift of the control valve member by the liquid pressure acting unopposed on the said small effective area.

12. In a hydraulic hammer, in combination, a body having a pair of chambers, a pressure liquid reciprocable differential area piston-hammer movably mounted in a first of said chambers, said piston-hammer having a land with a large surface area portion and an opposing small surface area portion, a control valve member movably mounted in the second of said chambers, means associated with said valve member providing opposed differential areas subject to pressure liquid with a large area effective at one end of the valve member and a small area effective at the other end, first passage means for connection to a source of pressure liquid to apply pressure liquid continuously against the small effective area of the control valve member and the small area portion of the piston-hammer by connection to a first end of said first chamber, second passage means connecting the first chamber at a port intermediate the ends thereof with the large effective area of the control valve member, third passage means connected to a second end of said first chamber remote from said first end and controlled by said control valve member for connecting the large surface area portion of the piston-hammer either to the source of pressure liquid or to tank, fourth passage means connected to said first chamber between said first end thereof and the connection of the second passage means to said first chamber and extending to said second chamber for communication with said third passage under the control of the control valve, said land on the piston-hammer operable during the impact stroke thereof to positively cut off the source of pressure liquid from said large surface area portion of the piston-hammer by blocking the fourth passage means and from the large effective area of the control valve member by blocking the second passage means, and said piston-hammer land after said positive cut-off of flow being effective upon continued movement to open the large effective area of the control valve member to the large surface area portion of the piston'hammer by traveling past the second passage means port whereby continued movement of the piston-hammer reduces pressure acting on the large effective area of the control valve member to permit shift of the control valve member by the liquid pressure acting unopposed on the said small effective area.

13. A hydraulic hammer as defined in claim 12 wherein said land is positioned on said piston-hammer to block the fourth passage means to cut-oft pressure liquid prior to striking the blow on the impact stroke.

14. A hydraulic hammer as defined in claim 12 and having a movable bumper at the second end of the first chamber for contact by the piston-hammer at the end of the return stroke thereof, and fifth passage means connecting a source of pressure liquid to the rear of said bumper whereby said bumper is urged toward the first chamber but can yield upon contact or when pressure builds up in the first chamber during return of the pistonhammer while the control valve is shifting.

15. A hydraulic hammer as defined in claim 14 including an accumulator connectible with a source of pressure liquid and said fifth passage means whereby pressure build-up behind said bumper is absorbed by said accumulator.

16. A hydraulic hammer as defined in claim 12 wherein said control valve member is hollow and open-ended to permit fluid flow therethrough while permitting quick shift thereof, and said means associated with the control valve member providing opposed differential areas comprises two pairs of pins with one pair engaging an end of the member to provide the small area, and the other pair of pins of a greater area providing the large area.

17. In a hydraulic tool, in combination, a body having a pair of chambers, a pressure liquid reciprocable differential area piston-hammer movably mounted in a first of said chambers, said piston-hammer having a large surface area portion and an opposing small surface area portion, a control valve member movably mounted in the second of said chambers, means associated with said valve member providing opposed differential areas subject to pressure liquid with a large area effective at one end of the valve member and a small area effective at the other end, first passage means for connection to a source of pressure liquid to apply pressure liquid continuously against the small effective area of the control valve member and the small area portion of the piston-hammer, second passage means connecting the first chamber with the large effective area of the control valve member, third passage means controlled by said control valve member for connecting the large surface area portion of the pistonhammer either to the source of pressure liquid or to tank, and said piston-hammer being effective to open the large effective area of the control valve member to the large surface area portion of the piston-hammer whereby continued movement of the piston-hammer reduces pressure acting on the large effective area of the control valve member to permit shift of the control valve member by the liquid pressure acting unopposed on the said small effective area.

References Cited UNITED STATES PATENTS 908,921 1/1909 Whitcomb 91235 1,430,764 10/1922 Smith 91-300 2,248,546 7/ 1941 Morrison et al. 91-321 3,207,043 9/1965 Kay 91-290 FOREIGN PATENTS 651,732 11/ 1962 Canada.

PAUL E. MASLOUSKY, Primary Examiner. 

1. IN AN IMPACT DEVICE, THE COMBINATION COMPRISING A BODY, SAID BODY HAVING A BORE, A PISTON-HAMMER RECIPROCABLE IN SAID BORE, SAID PISTON-HAMMER HAVING OPPOSED PRESSURE AREAS DEFINING FIRST AND SECOND PRESURE AREAS, SAID FIRST PRESSURE AREA HAVING AN EFFECTIVE CROSS SECTIONAL AREA LESS THAN SAID SECOND PRESSURE FLUID TO SAID MEANS FOR CONTINUOUSLY APPLYING PRESSURE FLUID TO SAID FIRST PRESSURE AREA, VALVE MEANS FOR ALTERNATELY APPLYING PRESSURE FLUID TO SAID SECOND PRESSURE AREA AND HAVING OPPOSED DIFFERENTIAL PRESSURE AREAS, MEANS FOR CONTINUOUSLY APPLYING PRESSURE FLUID TO THE SMALLER OF THE PRESSURE AREAS OF THE VALVE MEANS, AND MEANS INCLUDING THE PISTON-HAMMER FOR ALTERNATELY CONNECTING THE LARGER OF THE PRESSURE AREAS OF THE VALVE MEANS TO EITHER PRESSURE FLUID OR TO A DISCHARGE PATH AND FOR BLOCKING PRESSURE FLUID FROM THE SECOND PRESSURE AREA OF THE PISTON-HAMMER WHILE THE VALVE MEANS IS STILL POSITIONED TO SUPPLY PRESSURE FLUID THERETO TO TERMINATE THE APPLICATION OF FORCE TO THE PISTON-HAMMER. 